1. Field of the Invention
The present invention relates to improvements in vacuum-closure cans having non-nailed, easy-opening, metallic lids, for foodstuff packing.
2. Background Information
The can to which the present improvements relate is the object of Brazilian Patent BR No. 9203029 of Jul. 25, 1995 to the same inventor as this application. This patent essentially discloses a cylindrical body with a bottom wall normally fixed by nailing. The body includes, on its superior part and close to the top thereof, a round fillet outwardly turned that allows the can to be closed by a non-nailed, easy-opening metallic lid. The referred lid is the object of Brazilian Patent No. 9103896-0, of Feb. 1, 1994 to the same inventor. This lid essentially comprises a circular panel, presenting a descending edge or casing, provided with a narrow peripheral fillet. The lid is provided with a blocking gasket and, on the center of its panel, with a circular depression with a hollow center sealed by a resinous detachable seal.
The present invention would not be feasible without the pre-existing easy-opening lid, which has been successfully adopted in the closure of glass cups and pots. This kind of lid is used with the same practical advantages in a tinned food closure.
Both the easy-opening lid and can inventions discussed above, required great efforts and investments in research and experiments, including the creation of special equipment and new technologies to allow the manufacture of this package in high production scales.
This easy-opening can modified the traditional systems of metallic foodstuff packing closure, and distinguishes from others basically by not comprising any mechanical device for lid retention. The lid is kept closed only by atmospheric pressure. The closure is maintained by an elevated vacuum formed in the interior of the package.
These vacuum-closure cans with the non-nailed, easy-opening, metallic lids are distinguished from conventional cans by their practical and utilitarian aspects which focus not only on the manufacturers of foodstuff packings but particularly on the consumers, thanks to the safety and simplicity that they offer against accidents. Once the can is opened, it doesn't require any auxiliary device or extra effort. The lid is released by the aid of a simple extraction of the lid which is lifted with the nail edge and, subsequently removed by the user's fingers.
Some inconvenient aspects of the closure were found in practice, not only on the industrial operation lines but in storage, delivering and general manipulation of these cans. This is due to the delicate closing process which is obtained only by vacuum action and through the application of vapor spargers. A tinned product is, at this time, at a temperature higher than 194.degree. F.
As long as the canned product temperature is very high, the vapor-sparger closing machine naturally forms only a very low vacuum in the interior of the can. This provides, at this moment, a very low level of safety for the closure.
The industrial process for such cans includes the following sequential steps: filling, vacuum-closing, sterilizing and cooling. From one step to the next, the cans are transported in rows at high velocities in order to be automatically inserted into the corresponding machines, thereby provoking collisions among such cans. During this process, the peripheral fillets on the lids lift up one over another resulting in a bunch of accidental openings of the lids due to the low vacuum. This is illustrated in FIG. 5 and results in much lost production. It is impossible for the sealing machine to provide a higher vacuum while the product in the cans are at temperatures higher than 194.degree. F.
Such conditions cannot be modified during the closing process of the easy-opening cans mentioned above, as long as the vapor sparge as well as the canned product are above 194.degree. F. This requires the cans to be instantaneously closed to keep the vapor sparge in the free space that is formed above the product, in order to be condensed and, thereby form the initial vacuum.
Therefore these high temperatures resulting from the closing process of this kind of package cannot be modified because, as soon as the final process takes place, a high vacuum (which is responsible to the closure safety) will result from such temperatures.
Another problem with this kind of package is that whenever the closed cans--provided with a high vacuum and ready for transport and storage--are closely arranged and placed in the pasteboard boxes, they keep their peripheral fillets (placed on the lids) intimately supported and submitted to lifting up among themselves. The action of the weight of the stacked boxes provokes the effort of one fillet against another and the vibration during transport causes accidental opening of the cans, and, thus, total loss of the product within the opened can.